Invertebrates provide a critical source of dietary protein for human and non-human primates. In tropical forests, seasonal variation in food abundance presents obstacles for food acquisition and influences foraging patterns. Fluctuations in fruit abundance and consumption have been well documented, yet less is known of variation in insectivory. We studied the effects of rainfall and temperature variation on invertebrate abundance and consumption by Costa Rican capuchin monkeys (Cebus capucinus). From 2003-2011 we studied four free-ranging groups of capuchins in Sector Santa Rosa, Guanacaste. We quantified invertebrate consumption via primate behavioral observations and invertebrate abundance via arboreal and terrestrial sampling techniques. The peak in invertebrate consumption coincided with the onset of the rainy season and was primarily driven by dramatic increases in caterpillar populations. A trough in invertebrate consumption occurred with heavier rainfall and cooler temperatures. During the dry season, invertebrates were eaten in moderate amounts. At this time of year, consumption of large mobile (i.e. katydids, cockroaches) and embedded (i.e. termites, grubs) invertebrates increased. We suggest that the capuchins at our study site prefer caterpillars when they become available in the early rainy season, and bias their diet to reflect this. When available, caterpillars may be the most profitable invertebrates to target because they are harvested quickly and require shorter handling and processing times than other invertebrate types. Capuchins focus on more difficult-to-obtain invertebrates in the dry season when caterpillars are not available. Seasonal variation in invertebrate abundance has important implications for capuchin foraging energetics and food acquisition strategies.

This research was supported by funding from The Leakey Foundation (ADM), the Alberta Ingenuity Fund (ADM), the Natural Sciences and Engineering Research Council of Canada (ADM, HCY, LMF), the American Society of Primatologists (ADM), Sigma Xi (ADM, KNM, HCY) and the University of Calgary (ADM, KNM, HCY).